1. Field of the Invention
The invention relates to foundry and more particularly to apparatus for manufacturing foundry cores from fluid sands which are pressed into heated core boxes.
The invention can be used at sanitary engineering, machine building, electrical engineering, automotive production plants and in various industries of mass or large-lot scale of production.
2. Description of the Prior Art
A method and equipment, developed in the USSR, for manufacturing foundry cores by pressing fluid sands into heated core boxes are gaining an ever wider recognition at the present time. These innovations provide a means for obtaining single-piece cores with a natural internal canal ensuring an ideal removal of gases in the course of pouring.
There is known a machine for manufacturing cores from fluid sands (see FRG Pat. No. 2,239,057, Cl. B 22 C 9/10).
The machine comprises a sand preparation mechanism including a continuous-action mixer and a device for feeding starting sand components therein, a batching chamber, a damper with an expansible conical nozzle actuated by a compressed-air cylinder, a pressing cylinder with a plunger, a final pressing cylinder with a final pressing plunger, an elevator and a lifting table.
The machine operates in the manner below.
Fluid sand is fed from the mixer into the batching chamber, after which a mixer port is shut off by a special gate. The damper is moved by a compressed-air cylinder into a position where the conical nozzle secured thereon aligns itself with the batching chamber. The top diameter of the conical nozzle corresponds to the diameter of the batching chamber, and the bottom diameter, to that of an inlet orifice of a core box. A heated core box is forced by the table against the nozzle which is then contracted. The pressing piston is caused by the pressing cylinder to move downward and pack sand into the core box. Once this is completed, sand is given a final pressing by the final pressing plunger actuated by the final pressing cylinder. The diameter of the final pressing cylinder is somewhat smaller than that of the inlet orifice of the core box, and the cylinder is thus capable of penetrating inside the conical nozzle. After sealing, the core box is transferred to a drying station, a fresh core box being placed on the table. The damper is moved to initial position, flaps of the nozzle move apart, and remaining sand falls onto the elevator which returns them to the mixer.
The pressing and the final pressing cylinders raise their plungers into initial position, a special gate opens the port of the mixer and sand fills again the batching chamber.
As the diameter of the batching chamber is, as a rule, several times greater than the diameter of the inlet orifice of the core box, it is necessary to increase considerably the height and, therefore, the volume of the conical nozzle. Sand remaining in the nozzle loses its process properties, can no longer be used for filling another core box and must be removed before a next pressing takes place. When compressed, a sand which has lost its flowability sticks firmly to walls of the nozzle, so that it proves impossible to remove it without special cleaning devices.
The nozzle of the machine, consisting of two sliding parts actuated by cylinders, while being complicated in design, still fails to clean sand off the nozzle effectively. Another consideration is that the nozzle fails to contract tightly should some sand stick to the parting plane, this involving a risk of sand "leakage". Sand remaining in the nozzle, first, renders difficult the filling of the core box with a fresh portion of sand, and second, may fall as lumps into the core box and thus impair the quality of cores.
The use of the elevator in the known machine for returning unused sand to the mixer only complicates the machine, while failing to perform its function adequately. The underlying cause is that the sand possesses a high glueing ability, so that the elevator is "plugged" and thus disabled in a short length of time.
Guides, wherein the gate slides, are blocked with sand when the gate is in top position, so that no reliable closing of the port of the mixer and isolation of the batching chamber from the mixer are obtainable.
Still another shortcoming of the machine is its sliding damper with a nozzle secured thereto. When sand is pressed into the core box through an inlet orifice whose cross sectional area is many times smaller than that of the batching chamber, the pressure therein rises and forces sand out through all the gaps, including those between the batching chamber and the damper. These gaps are also penetrated by sand from the batching chamber when the damper with the nozzle slides into working position. Sand blocking the gaps rapidly hardens in the air, heat radiation from the heated core boxes enhancing the process. This results in frequent blocking of the damper, stoppage of the machine for cleaning rubbing surfaces from stuck sand.
The final pressing operation in the known machine provides no beneficial effect and not only complicates the design and the efficiency thereof, but also over-packs core prints to hinder the formation of voids therein and the communication thereof with the atmosphere using vent wires.
Still another shortcoming of the machine is a lack of means for metering (adjusting the volume of the batching chamber) fluid sand over a wide range and manufacturing, without re-conversion, cores substantially (by two and more times) differing in weight.
The lack of sand metering makes it impossible to manufacture quality cores of any specified mass, to stabilize the weight of cores and the size of the natural canal, to minimize or eliminate altogether waste of sand.
Process potentialities of the machine and the range (by weight) of cores manufactured thereby are reduced by the lack of sand metering.
Changing the machine from the manufacture of one type of cores to another requires re-conversion which consists in the replacement of subassemblies (batching chamber, pressing plunger and others) of the machine, complete replacement of one set of core boxes and necessitates much time. The fact that no cores differing in weight can be manufactured simultaneously on the machine calls for a substantial increase in the number of core boxes.